1. Field of the Invention
The present invention relates to a method of operating a winch, in which a rope which is wound onto a driven reel is supplied to at least one capstan head and is wound around said capstan head, with a capstan drive rotating the capstan head and producing a rope advance due to the rope friction existing between rope and capstan head. Furthermore, the present invention relates to a corresponding winch.
2. Description of the Prior Art
Winches of this type are, for instance, used in piste maintaining devices as climbing aids for climbing steep pistes. The rope is wound around the capstan head or capstan heads once or several times and is hauled in by the reel drum. The vehicle is advanced by rotating the capstan head due to the static friction produced by the rope being wound around the capstan heads.
In a winch which is known in practice, the reel and the capstan head are each provided with a hydraulic motor which is driven by a joint hydraulic pump. This ensures that, when the capstan head is driven, the rope is continuously received from the reel and the necessary winding around the capstan head is simultaneously maintained. In practice, however, problems have arisen from the reel winding. The rope is very tightly wound onto the reel, and it may happen that the rope gets pinched between two windings of a lower rope layer when being wound up. Moreover, there is the risk that the rope will not properly travel in the axial direction of the reel, but is wound in an untidy manner as a bulging portion onto a reel section.
It is the object of the present invention to improve the generic method, as well as the winch associated therewith, in such a manner that the rope can be wound without any problems onto the reel and that an effective rope advance for a good drive is made possible by the winch at the same time, the winch being operable in a manner which is as simple and reliable as possible.
This object is achieved according to the invention with a generic method which is characterized in that the reel drive is adjusted separately next to the capstan drive.
As a consequence, the reel drive can be better optimized to the function of winding and unwinding the rope, so that the rope can be received on a reel without any problem. Apart from this, the capstan drive can be optimized in accordance with the required tractive power or advance power of the vehicle. The reel drive ensures an adequate rope tension for maintaining the winding around the capstan head as is required for the advance movement.
Surprisingly enough, it has been found in practice that a tidy winding onto the reel is possible thanks to this sectionwise separation of the drives. Moreover, this improves efficiency, since power losses between capstan head and reel are minimized thanks to the separate adjustment and thanks to a possible improved adaptation of the members.
While it has so far been assumed throughout the prior art that the drives of reel and capstan head must be intregrally formed and adjusted to achieve an optimum cooperation of the two elements, the present invention shows an approach in which use is made of separate adjustments or controls and an improved cooperation of the elements is nevertheless possible.
In an especially advantageous manner the reel can be driven in accordance with the necessary tensile force of the rope between reel and capstan head. This results in the achievement of an optimum tractive force between capstan head and reel. The tractive force can be adapted such that there is enough static friction for the advance movement on the capstan head and enough traction for an orderly winding of the rope onto the reel. The tensile force, however, can be kept below a critical range which, if exceeded, would result in problems with the winding. The tensile force, for instance, may be at about 700 N, which is a suitable value for winches of piste maintaining devices.
The displacement volume of a hydraulic pump which is connected to a hydraulic motor driving the reel can be adjusted in a specific manner in response to the load condition of the hydraulic motor. As a result, the drive of the reel can very well be optimized for an optimum tensile force of the rope between reel and capstan head. When the force of the rope increases excessively, the displacement volume can be reduced, so that the tensile force will no longer increase. In the case of a slack rope the displacement volume can be increased, so that the rope is wound up rapidly and up to an optimum tension. The load condition of the hydraulic motor respectively results from the resistance transmitted by the reel drum to the motor. With the aid of the hydraulic pump the drive of the hydraulic motor can be adjusted or controlled in an optimum manner by a corresponding adjustment.
Preferably, the load pressure can be kept substantially constant under different load conditions in a hydraulic line which is provided between a hydraulic motor driving the reel and the hydraulic pump driving the motor. The drive power can very well be controlled by this measure. At the same time, this measure prevents the occurrence of excessive torques on the reel. The drive power can very well be varied in the hydraulic pump just by adjusting the displacement volume.
In a variant of the invention, the control circuit of the reel drive can be activated separately. This is especially of advantage when the system is started, since the adjustment or control need only be activated upon start of the rope operation. Prior to this activation a low standby pressure could, for instance, be set in the reel system. It is only upon the winch operation proper that a control operation with the necessary operative pressure for ensuring the necessary minimum torques can be started by activating the reel drive.
A motor of the reel drive might be operated as a resistance-producing pump when the rope is being pulled from the reel. When the rope is being pulled, this ensures a sufficient counter-force which will slightly tighten the rope and supply the sane to the capstan head.
In a special embodiment, the capstan drive can be controlled independently of the reel drive according to the necessary rope advance. As a result, the desired drive force or drive speed of the capstan drive can be controlled separately, so that the reel drive need not be taken into account. Hence, it adjusts automatically. As a consequence, upon operation of the winch drive, the advance movement can be concentrated on.
It is possible to change the displacement volume of a hydraulic pump with the aid of and under separate control of the load pressure produced by the hydraulic pump, with the latter being connected to the hydraulic motor driving the capstan head. Hence, the load pressure can be used for controlling the pump. The load pressure can then be varied accordingly in a branch line and can be made use of in a correspondingly controlling manner for adjusting the said pump.
A reel brake and a capstan head brake can especially advantageously be released at the same time when the winch drive is started. Hence, reel and capstan head are locked in the inoperative state by the brakes and they are only released upon start of the winch drive, with the corresponding torques starting the rope advance and the rope winding action at the same time. When the winch drive is stopped, both brakes, for instance, can lock again, so that the rope will remain taught between capstan head and reel in an optimum manner for the next use.
In a variant of the invention, the brakes can be operated in response to an operative pressure in a hydraulic line of the reel drive. The brakes can only be released optionally if an operative pressure in the reel drive has been exceeded, so that the reel will only be released if enough torques are already present at the reel drive for maintaining the rope tension. The operative pressure serves as a regulating means for a sufficient torque. On the other hand, the reel brake or also the capstan head brake will lock again when an operative pressure is not reached, so that the rope is kept in its taught state.
Possibly, the brakes can only be released after a torque has been applied to the reel. As a consequence, the reel drum is released and a suitable torque for the winding action and for the rope tension is alreadly available at the time of release.
When rope and reel are replaced, a reel brake may be released in a special manner by actuating means which are separated from the drive. Therefore, even if the drive or the vehicle is at a standstill, the reel can be released from the outside for changing the rope.
In a preferred embodiment the capstan drive may be blocked during change of the rope. This ensures that the rope advance is at a standstill when the rope is being replaced.
The above-described generic method can, for instance, be realized by a generic winch which comprises a reel which is driven by a reel drive and onto which the rope can be wound and from which the rope can be unwound, with the rope being adapted to be supplied from the reel to at least one capstan head and being adapted to be wound around said head, and a capstan drive rotating the capstan head and advancing the rope because of rope friction with the capstan head.
The above-mentioned object arises in such a generic winch.